Coated articles and methods comprising a rhodium layer

ABSTRACT

Coated articles and methods for applying coatings including a rhodium layer are described. In some cases, the coating can exhibit desirable properties and characteristics such as durability, corrosion resistance, and high conductivity. The articles may be coated, for example, using an electrodeposition process.

FIELD OF INVENTION

The present invention generally relates to coated articles comprising a rhodium layer and related methods. In some embodiments, the articles are coated using an electrodeposition process.

BACKGROUND OF INVENTION

Many types of coatings may be applied on a base material. Electrodeposition is a common technique for depositing such coatings. Electrodeposition generally involves applying a voltage to a base material placed in an electrodeposition bath to reduce metal ionic species within the bath which deposit on the base material in the form of a metal, or metal alloy, coating. The voltage may be applied between an anode and a cathode using a power supply. At least one of the anode or cathode may serve as the base material to be coated. In some electrodeposition processes, the voltage may be applied as a complex waveform such as in pulse plating, alternating current plating, or reverse-pulse plating.

A variety of metal and metal alloy coatings may be deposited using electrodeposition. For example, metal alloy coatings can be based on two or more transition metals including Ni, W, Fe, Co, amongst others.

Corrosion processes, in general, can affect the structure and composition of an electroplated coating that is exposed to the corrosive environment. For example, corrosion can involve direct dissolution of atoms from the surface of the coating, a change in surface chemistry of the coating through selective dissolution or de-alloying, or a change in surface chemistry and structure of the coating through, e.g., oxidation or the formation of a passive film. Some of these processes may change the topography, texture, properties, or appearance of the coating. For example, spotting and/or tarnishing of the coating may occur. Such effects may be undesirable, especially when the coating is applied at least in part to improve electrical conductivity since these effects can increase the resistance of the coating.

SUMMARY OF INVENTION

Coated articles comprising a rhodium layer and related methods are provided.

In some embodiments, articles are provided. In some embodiments, an article comprises a base material, a barrier layer formed on the base material, a metal layer formed on the barrier layer, and a Rh layer formed on the metal layer and having a thickness between about 1 microinch and about 5 microinches.

In some embodiments, methods are provided. In some embodiments, a method comprises electrodepositing a barrier layer on a base material; electrodepositing a metal layer on the barrier layer; and electrodepositing a Rh layer on the metal layer, wherein the Rh layer has a thickness between about 1 microinch and about 5 microinches.

Other aspects, embodiments, and features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. The accompanying figures are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. All patent applications and patents incorporated herein by reference are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a coated article, according to some embodiments.

DETAILED DESCRIPTION

Coated articles comprising a rhodium layer and methods for applying coatings are described. The article may include a base material and a multi-layer coating formed thereon. In some embodiments, the coating includes a base material, a barrier layer formed on the base material, a metal layer formed on the barrier material, and a rhodium layer formed on the metal layer. In some cases, the barrier layer comprises an alloy (e.g., nickel alloy, silver alloy) and the metal layer comprises a precious metal (e.g., Ru, Rh, Os, Ir, Pd, Pt, Ag, and/or Au). In some cases, the coating may be applied using an electrodeposition process. The coating can exhibit desirable properties and characteristics such as durability, corrosion resistance, and high conductivity, which may be beneficial, for example, in electrical applications.

FIG. 1 shows an article 10 according to a non-limiting embodiment. The article has coating 20 formed on a base material 30. The coating may comprise barrier layer 40 formed on the base material, metal layer 50 formed on the barrier layer, and rhodium layer 60 formed on the metal layer. Each layer may be applied using a suitable process, as described in more detail below. It should be understood that the coating may include more than three layers. However, in some embodiments, the coating may only include three layers, as shown.

The inventors have discovered that formation of a rhodium layer on a metal layer results in articles with desired properties as compared to articles formed comprising only the metal layer. For example, the presence of a metal layer and a rhodium layer on an article as compared to only a metal layer leads to improved coloration (e.g., desired shade/tone, color stability over time, etc.), improved durability, and/or improved corrosion resistance.

In some embodiments, the rhodium layer has a thickness greater than about 1 microinch. In some cases, the rhodium layer has a thickness between about 1 microinch and about 5 microinches. The inventors have discovered that coated articles comprising a rhodium layer having a thickness less than about 1 microinch or greater than about 5 microinches can result in inferior performance. For example, rhodium layers having a thickness less than 1 microinch may provide incomplete coverage of the metal layer which can affect the overall coating appearance (e.g., may affect the color stability overtime), wear performance, and/or corrosion resistance. For example, rhodium layers having a thickness greater than 5 microinches can have highly stressed and/or cracked deposits which can affect the coating appearance and/or wear performance.

In some embodiments, the barrier layer comprises one or more metals. The barrier layer is generally comprised of a layer that is conductive. In some cases, the barrier layer comprises a material that has some corrosion resistance to the conditions under which the article is to be employed. In some cases, the barrier layer acts as a diffusion barrier between the base material and subsequent layers of material. In some cases, the barrier layer comprises nickel or consists essentially of nickel. In some cases, the barrier layer comprises silver or consists essentially of silver. In some cases, the barrier layer comprises palladium or consists essentially of palladium. In some cases, the barrier layer comprises a metal alloy. In some cases, alloys that comprise nickel (e.g., nickel-tungsten alloys) or silver (e.g., silver, tungsten, and/or molybdenum) are preferred.

In some embodiments, the barrier layer comprises a nickel alloy (i.e., nickel-based alloys). Nickel alloys are known in the art. For example, see U.S. Publication No. 2011/0008646 by Cahalen et al., filed Jul. 10, 2009, and U.S. Publication No. 2012/0328904 by Baskin et al., filed Jun. 22, 2012, each herein incorporated by reference. In some cases, the nickel-alloy further comprises tungsten and/or molybdenum (e.g., a nickel-tungsten alloy, a nickel-molybdenum alloy, a nickel-tungsten-molybdenum alloy). Other nickel alloys may also be employed. For example, the nickel alloy may further comprise cobalt, phosphorus, and/or palladium. In some cases, the weight percent of nickel in the alloy may be between 25-75 weight percent; and, in some cases, between 50 and 70 weight percent. In these cases, the remainder of the alloy may be tungsten and/or molybdenum. Other weight percentages outside of this range may be used as well. For example, in some embodiments and for certain applications, the weight percent of tungsten in the alloy may be greater than or equal to 10 weight percent; in some cases, greater than or equal to 14 weight percent; in some cases, greater than or equal to 15 weight percent; and, in some cases greater than or equal to 20 weight percent. In some cases, the total weight percentage of tungsten in the alloy is less than or equal to 35 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 30 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 28 weight percent; and, the total weight percentage of tungsten in the alloy is less than or equal to 25 weight percent.

In some embodiments, the barrier layer comprises a silver alloy (i.e., silver-based alloys). Such alloys may also comprise tungsten and/or molybdenum. Silver alloys are known in the art, for example, see U.S. Publication No. 2011/0223442 by Dadvand et al., filed Mar. 12, 2010, herein incorporated by reference. In some embodiments, the barrier layer comprises a silver-tungsten alloy. Other silver alloys may also be employed. In some cases, the atomic percent of tungsten and/or molybdenum in the alloy may be between 0.1 atomic percent and 50 atomic percent; and, in some cases, between 0.1 atomic percent and 20 atomic percent, the remainder being silver. In some embodiments, the atomic percent of tungsten and/or molybdenum in the alloy may be at least 0.1 atomic percent, at least 1 atomic percent, at least 1.5 atomic percent, at least 5 atomic percent, at least 10 atomic percent, or at least 20 atomic percent, the remainder being silver. Other atomic percentages outside of this range may be used as well.

The barrier layer may have a thickness suitable for a particular application. For example, the barrier layer thickness may be greater than about 1 microinch (e.g., between about 1 microinch and about 250 microinches, between about 1 microinch and about 200 microinches, between about 1 microinch and about 150 microinches, between about 1 microinch and about 100 microinches, between about 1 microinch and 50 microinches); in some cases, greater than about 5 microinches (e.g., between about 5 microinches and about 100 microinches, between about 5 microinches and 50 microinches); greater than about 25 microinches (e.g., between about 25 microinches and about 100 microinches, between about 1 microinch and 50 microinches). It should be understood that other barrier layer thicknesses may also be suitable. Thickness may be measured by techniques known to those in the art.

In some embodiments, it may be preferable for the barrier layer to be formed directly on the base material. Such embodiments may be preferred over certain prior art constructions that utilize a layer between the barrier layer and the base material because the absence of such an intervening layer can save on overall material costs. Though, it should be understood that in other embodiments, one or more layers may be formed between the barrier layer and the base material.

The metal layer may comprise one or more precious metals. Examples of suitable precious metals include Ru, Rh, Os, Ir, Pd, Pt, Ag, and/or Au. In some embodiments, the precious metal is selected from the group consisting Ru, Os, Ir, Pd, Pt, Ag, and Au, or combinations thereof. Gold may be preferred in some embodiments. In some embodiments, the metal layer consists essentially of one precious metal. In some embodiments, it may be preferable that the metal layer is free of tin. In some cases, the precious metal is not rhodium. In other cases, the metal layer may comprise an alloy that includes at least one precious metal and at least one other metal. The other metal may be selected from Ni, W, Fe, B, S, Co, Mo, Cu, Cr, Zn, and Sn, amongst others.

In some embodiments, the metal layer comprises a silver alloy (i.e., silver-based alloys). Such alloys may also comprise tungsten and/or molybdenum. Silver alloys are known in the art, for example, see U.S. Publication No. 2011/0223442 by Dadvand et al., filed Mar. 12, 2010, herein incorporated by reference. In some embodiments, the barrier layer comprises a silver-tungsten alloy. Other silver alloys may also be employed. In some cases, the atomic percent of tungsten and/or molybdenum in the alloy may be between 0.1 atomic percent and 50 atomic percent; and, in some cases, between 0.1 atomic percent and 20 atomic percent, the remainder being silver. In some embodiments, the atomic percent of tungsten and/or molybdenum in the alloy may be at least 0.1 atomic percent, at least 1 atomic percent, at least 1.5 atomic percent, at least 5 atomic percent, at least 10 atomic percent, or at least 20 atomic percent, the remainder being silver. Other atomic percentages outside of this range may be used as well.

In some embodiments, the metal layer comprises a silver-based alloy and the barrier layer comprises a nickel-based alloy. In some cases, the metal layer comprises a silver-based alloy further comprising molybdenum and/or tungsten and the barrier layer comprises a nickel-based alloy further comprising molybdenum and/or tungsten. In some cases, the metal layer comprises a silver-tungsten alloy and the barrier layer comprises a nickel-tungsten alloy.

The metal layer may have any suitable thickness. It may be advantageous for the metal layer to be thin, for example, to save on material costs. For example, the metal layer thickness may be less than 30 microinches (e.g., between about 1 microinch and about 30 microinches; in some cases, between about 5 microinches and about 30 microinches); in some cases the metal layer thickness may be less than 20 microinches (e.g., between about 1 microinch and about 20 microinches; in some cases, between about 5 microinches and about 20 microinches); and, in some cases, the metal layer thickness may be less than 10 microinches (e.g., between about 1 microinch and about 10 microinches; in some cases, between about 5 microinches and about 10 microinches). It should be understood that other metal layer thicknesses may also be suitable.

In some embodiments, it may preferable for the metal layer to be formed directly on the barrier material. Such embodiments may be preferred over certain prior art constructions that utilize a layer between the metal layer and the barrier material because the absence of such an intervening layer can save on overall material costs. Though, it should be understood that in other embodiments, one or more layers may be formed between the metal layer and the barrier material.

The metal layer may cover the entire barrier layer. However, it should be understood that in other embodiments, the metal layer covers only part of the barrier layer. In some cases, the metal layer covers at least 50% of the surface area of the barrier layer; in other cases, at least 75% of the surface area of the barrier layer. In some cases, an element from the barrier layer may be incorporated within the metal layer and/or an element from the metal layer may be incorporated into the barrier layer.

In some cases, the coating (e.g., the barrier layer, rhodium layer, and/or the metal layer) may have a particular microstructure. For example, at least a portion of the coating may have a nanocrystalline microstructure. As used herein, a “nanocrystalline” structure refers to a structure in which the number-average size of crystalline grains is less than one micron. The number-average size of the crystalline grains provides equal statistical weight to each grain and is calculated as the sum of all spherical equivalent grain diameters divided by the total number of grains in a representative volume of the body. The number-average size of crystalline grains may, in some embodiments, be less than 100 nm (e.g., 1 nm to 100 nm). In some embodiments, at least a portion of the coating may have an amorphous structure. As known in the art, an amorphous structure is a non-crystalline structure characterized by having no long range symmetry in the atomic positions. Examples of amorphous structures include glass, or glass-like structures. Some embodiments may provide coatings having a nanocrystalline structure throughout essentially the entire coating. Some embodiments may provide coatings having an amorphous structure throughout essentially the entire coating.

In some embodiments, the coating may comprise various portions having different microstructures. For example, the barrier layer may have a different microstructure than the metal layer and/or the rhodium layer. The coating may include, for example, one or more portions having a nanocrystalline structure and one or more portions having an amorphous structure. In one set of embodiments, the coating comprises nanocrystalline grains and other portions which exhibit an amorphous structure. In some cases, the coating, or a portion thereof (i.e., a portion of the barrier layer, a portion of the metal layer, a portion of the rhodium layer, or a portion of two of the layers, or all three of the layers), may comprise a portion having crystal grains, a majority of which have a grain size greater than one micron in diameter. In some embodiments, the coating may include other structures or phases, alone or in combination with a nanocrystalline portion or an amorphous portion. Those of ordinary skill in the art would be able to select other structures or phases suitable for use in the context of the invention.

Advantageously, the coating (i.e., the barrier layer, the metal layer, the rhodium layer, or two of the layers, or all three of the layers) may be substantially free of elements or compounds having a high toxicity or other disadvantages. In some instances, it may also be advantageous for the coating to be substantially free of elements or compounds that are deposited using species that have a high toxicity or other disadvantages. For example, in some cases, the coating is free of chromium (e.g., chromium oxide), which is often deposited using chromium ionic species that are toxic (e.g., Cr⁶⁺). Such coating may provide various processing, health, and environmental advantages over certain previous coatings.

In some embodiments, metal, non-metal, and/or metalloid materials, salts, etc. (e.g., phosphate or a redox mediator such as potassium ferricyanide, or fragment thereof) may be incorporated into the coating.

The composition of the coatings, or portions or layers thereof, may be characterized using suitable techniques known in the art, such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), etc. For example, AES and/or XPS may be used to characterize the chemical composition of the surface of the coating.

Base material 30 may be coated to form coated articles, as described above. In some cases, the base material may comprise an electrically conductive material, such as a metal, metal alloy, intermetallic material, or the like. Suitable base materials include steel, copper, aluminum, brass, bronze, nickel, polymers with conductive surfaces and/or surface treatments, transparent conductive oxides, amongst others. In some embodiments, copper base materials are preferred.

In some embodiments, a lubricant layer may be formed as an upper portion of the coating. The lubricant layer may comprise, for example, an organic material, a self-assembled monolayer, carbon nanotubes, and the like. In some cases, the presence of a lubricant layer reduces the coefficient of friction of the coating as compared to a substantially similar coating but which does not include the lubricant layer. The lubricant layer may be formed of any suitable material, for example halogen-containing organic lubricant, a polyphenyl-containing organic lubricant, or a polyether-containing lubricant. In one embodiment, the lubricant layer is formed of a halogen-containing organic lubricant. Specific non-limiting examples of lubricants include Evabrite™ (Enthone), Au lube (AMP), NyeTact® 570H (Nye Lubricants), FS-5 (Gabriel Performance Products), S-30 (Gabriel Performance Products), and MS-383H (Miller-Stephenson). Another non-limiting example of a lubricant is chlorotrifluoroethylene. In some cases, the lubricant layer comprises a monolayer formed on the surface of the coating. In some cases, the lubricant may be as described in U.S. Publication No. 2012/0118755 to Dadvand et al., filed Sep. 14, 2011 or U.S. Publication No. 2012/0121925 by Trenkle et al., filed Sep. 14, 2011, herein incorporated by reference.

Those of ordinary skill in the art will be aware of suitable methods for forming a lubricant layer on a coating. For example, in some embodiments, an article comprising the coating may exposed (e.g., dipped into) to the lubricant (e.g., optionally in a solution), and the article may then be allowed to dry, thereby forming the lubricant layer on the upper portion of the coating.

In some embodiments, an article comprising a lubricant layer formed on coating may have a reduced coefficient of friction as compared to a substantially similar article which does not comprise the lubricant layer. In some cases, the article having the lubricant layer has a co-efficient of friction which is at least two times less, at least three times less, at least four times less, at least five times less, or at least ten times less than an article which not having the lubricant layer.

In some cases, an article having a lubricant layer may have better wear durability as compared to a substantially similar article which does not have a lubricant layer. Those of ordinary skill in the art will be aware of suitable methods to determine the wear durability of a material (e.g., ball-on-plate-type reciprocating friction abrasion test, wherein the ball and plate both are coated with a layer of the alloy, and optionally the lubricant layer). For example, in some embodiments, minimal or no wear-through may be observed for an article comprising a silver-based alloy and a lubricant layer over 50 cycles, 100 cycles, 250 cycles, 500 cycles, or 1000 cycles, with a 100 g applied load, wherein a substantially similar article which does not comprise the lubricant layer may show substantial or complete wear-through.

The articles can be used in a variety of applications including electrical applications such as electrical connectors (e.g., plug-type). The coating can impart desirable characteristics to an article, such as durability, corrosion resistance, and improved electrical conductivity. These properties can be particularly advantageous for articles in electrical applications such as electrical connectors, which may experience rubbing or abrasive stress upon connection to and/or disconnection from an electrical circuit that can damage or otherwise reduce the conductivity of a conductive layer on the article. Non-limiting examples of electrical connectors include infrared connectors, USB connectors, battery chargers, battery contacts, automotive electrical connectors, etc. In some embodiments, the presence of the first layer of a coating may provide at least some of the durability and corrosion resistance properties to the coating. In some embodiments, the coating may impart decorative qualities.

The coatings described herein may impart advantageous properties to an article, such as an electrical connector. In some embodiments, the coating, or layer of the coating, may have a low electrical resistivity. For example, the electrical resistivity may be less than 100 microohm-centimeters, less than 50 microohm-centimeters, less than 10 microohm-centimeters, or less than 2 microohm-centimeters.

The coating or layer of the coating may have a hardness of at least 1 GPa, at least 1.5 GPa, at least 2 GPa, at least 2.5 GPa, or at least 3 GPa. Those of ordinary skill in the art would readily be able to measure these properties.

Coating 20 may be formed using an electrodeposition process. Electrodeposition generally involves the deposition of a material (e.g., electroplate) on a substrate by contacting the substrate with an electrodeposition bath and flowing electrical current between two electrodes through the electrodeposition bath, i.e., due to a difference in electrical potential between the two electrodes. For example, methods described herein may involve providing an anode, a cathode, an electrodeposition bath (also known as an electrodeposition fluid) associated with (e.g., in contact with) the anode and cathode, and a power supply connected to the anode and cathode. In some cases, the power supply may be driven to generate a waveform for producing a coating, as described more fully below.

Generally, the barrier layer, the metal layer, and the rhodium layer of the coating may be applied using separate electrodeposition baths. In some cases, individual articles may be connected such that they can be sequentially exposed to separate electrodeposition baths, for example in a reel-to-reel process. For instance, articles may be connected to a common conductive substrate (e.g., a strip). In some embodiments, each of the electrodeposition baths may be associated with separate anodes and the interconnected individual articles may be commonly connected to a cathode.

The electrodeposition process(es) may be modulated by varying the potential that is applied between the electrodes (e.g., potential control or voltage control), or by varying the current or current density that is allowed to flow (e.g., current or current density control). In some embodiments, the coating may be formed (e.g., electrodeposited) using direct current (DC) plating, pulsed current plating, reverse pulse current plating, or combinations thereof. In some embodiments, reverse pulse plating may be preferred, for example, to form the barrier layer (e.g., nickel-tungsten alloy). Pulses, oscillations, and/or other variations in voltage, potential, current, and/or current density, may also be incorporated during the electrodeposition process, as described more fully below. For example, pulses of controlled voltage may be alternated with pulses of controlled current or current density. In general, during an electrodeposition process an electrical potential may exist on the substrate (e.g., base material) to be coated, and changes in applied voltage, current, or current density may result in changes to the electrical potential on the substrate. In some cases, the electrodeposition process may include the use waveforms comprising one or more segments, wherein each segment involves a particular set of electrodeposition conditions (e.g., current density, current duration, electrodeposition bath temperature, etc.), as described more fully below.

Some embodiments of the invention involve electrodeposition methods wherein the grain size of electrodeposited materials (e.g., metals, alloys, and the like) may be controlled. In some embodiments, selection of a particular coating (e.g., electroplate) composition, such as the composition of an alloy deposit, may provide a coating having a desired grain size. In some embodiments, electrodeposition methods (e.g., electrodeposition conditions) described herein may be selected to produce a particular composition, thereby controlling the grain size of the deposited material. The methods of the invention may utilize certain aspects of methods described in U.S. Patent Publication No. 2006/02722949, entitled “Method for Producing Alloy Deposits and Controlling the Nanostructure Thereof using Negative Current Pulsing Electro-deposition, and Articles Incorporating Such Deposits” and U.S. application Ser. No. 12/120,564, entitled “Coated Articles and Related Methods,” filed May 14, 2008, which are incorporated herein by reference in their entirety. Aspects of other electrodeposition methods may also be suitable including those described in U.S. Patent Publication No. 2006/0154084 and U.S. application Ser. No. 11/985,569, entitled “Methods for Tailoring the Surface Topography of a Nanocrystalline or Amorphous Metal or Alloy and Articles Formed by Such Methods,” filed Nov. 15, 2007, which are incorporated herein by reference in their entireties. In some embodiments, a nickel-based alloy and/or metal coating may be electrodeposited according to the methods described in U.S. Publication No. 2011/0008646 by Cahalen et al., filed Jul. 10, 2009, and/or U.S. Publication No. 2012/0328904 by Baskin et al., filed Jun. 22, 2012, each herein incorporated by reference. In some embodiments, a silver-based alloy and/or metal coating may be electrodeposited according to the methods described in U.S. Publication No. 2011/0223442 by Dadvand et al., filed Mar. 12, 2010, herein incorporated by reference.

In some embodiments, a coating, or portion thereof, may be electrodeposited using direct current (DC) plating. For example, a substrate (e.g., electrode) may be positioned in contact with (e.g., immersed within) an electrodeposition bath comprising one or more species to be deposited on the substrate. A constant, steady electrical current may be passed through the electrodeposition bath to produce a coating, or portion thereof, on the substrate. In some embodiments, the potential that is applied between the electrodes (e.g., potential control or voltage control) and/or the current or current density that is allowed to flow (e.g., current or current density control) may be varied. For example, pulses, oscillations, and/or other variations in voltage, potential, current, and/or current density, may be incorporated during the electrodeposition process. In some embodiments, pulses of controlled voltage may be alternated with pulses of controlled current or current density. In some embodiments, the coating may be formed (e.g., electrodeposited) using pulsed current electrodeposition, reverse pulse current electrodeposition, or combinations thereof.

In some cases, a bipolar waveform may be used, comprising at least one forward pulse and at least one reverse pulse, i.e., a “reverse pulse sequence.” As noted above, the electrodeposition baths described herein are particularly well suited for depositing coatings using complex waveforms such as reverse pulse sequences. In some embodiments, the at least one reverse pulse immediately follows the at least one forward pulse. In some embodiments, the at least one forward pulse immediately follows the at least one reverse pulse. In some cases, the bipolar waveform includes multiple forward pulses and reverse pulses. Some embodiments may include a bipolar waveform comprising multiple forward pulses and reverse pulses, each pulse having a specific current density and duration. In some cases, the use of a reverse pulse sequence may allow for modulation of composition and/or grain size of the coating that is produced.

A coating may be applied using an electrodeposition process at a current density of at least 0.001 A/cm², at least 0.01 A/cm², or at least 0.02 A/cm². Current densities outside these ranges may be used as well. In some cases, a direct current is employed having a direct current density of greater than about 10 mA/cm², greater than about 15 mA/cm², greater than about 20 mA/cm², greater than about 30 mA/cm², or greater than about 50 mA/cm².

For current which is applied in pulses, the frequency may be any suitable frequency (e.g., between 0.1 Hertz and about 100 Hz). Similarly, the voltage may be any suitable voltage (e.g., between about 0.1 V and about 1 V).

The deposition rate of the coating may be controlled. In some instances, the deposition rate may be at least 0.1 microns/minute, at least 0.3 microns/minute, at least 1 micron/minute, or at least 3 microns/minute. Deposition rates outside these ranges may be used as well.

Those of ordinary skill in the art would recognize that the electrodeposition processes described herein are distinguishable from electroless processes which primarily, or entirely, use chemical reducing agents to deposit the coating, rather than an applied voltage. The electrodeposition baths described herein may be substantially free of chemical reducing agents that would deposit coatings, for example, in the absence of an applied voltage.

The electrodeposition processes use suitable electrodeposition baths. Such baths typically include species that may be deposited on a substrate (e.g., electrode) upon application of a current. For example, an electrodeposition bath comprising one or more metal species (e.g., metals, salts, other metal sources) may be used in the electrodeposition of a coating comprising a metal (e.g., an alloy). In some cases, the electrochemical bath comprises nickel species (e.g., nickel sulfate) and tungsten species (e.g., sodium tungstate) and may be useful in the formation of, for example, nickel-tungsten alloy coatings.

Typically, the electrodeposition baths comprise an aqueous fluid carrier (e.g., water). However, it should be understood that other fluid carriers may be used in the context of the invention, including, but not limited to, molten salts, cryogenic solvents, alcohol baths, and the like. Those of ordinary skill in the art would be able to select suitable fluid carriers for use in electrodeposition baths. The pH of the electrodeposition bath can be from about 2.0 to 12.0. In some cases, the electrodeposition bath may be selected to have a pH from about 7.0-9.0. In some cases, the electrodeposition bath may have a pH from about 7.6 to 8.4, or, in some cases, from about 7.9 to 8.1. However, it should be understood that the pH may be outside the above-noted ranges. The pH of the bath may be adjusted using any suitable agent known to those of ordinary skill in the art. In some embodiments, the pH of the bath is adjusted using a base, such as a hydroxide salt (e.g., potassium hydroxide). In some embodiments, the pH of the bath is adjusted using an acid (e.g., nitric acid).

The electrodeposition baths may include other additives, such as wetting agents, complexing agents, brightening or leveling agents, and the like. Those of ordinary skill in the art would be able to select appropriate additives for use in a particular application.

In some embodiments, the electrodeposition bath may comprise at least one complexing agent (i.e., a complexing agent or mixture of complexing agents). A complexing agent refers to any species which can coordinate with the ions contained in the solution. In some embodiments, a complexing agent or mixture of complexing agents may permit codeposition of at least two elements.

In some cases, the baths may include at least one wetting agent. A wetting agent refers to any species capable of reducing the surface tension of the electrodeposition bath and/or increasing the ability of gas bubbles to detach from surfaces in the bath. For example, the substrate may comprise a hydrophilic surface, and the wetting agent may enhance the compatibility (e.g., wettability) of the bath relative to the substrate. In some cases, the wetting agent may also reduce the number of defects within the metal coating that is produced. The wetting agent may comprise an organic species, an inorganic species, an organometallic species, or combinations thereof. In some embodiments, the wetting agent may be selected to exhibit compatibility (e.g., solubility) with the electrodeposition bath and components thereof.

In some embodiments, the baths may include at least one brightening agent. The brightening agent may be any species that, when included in the baths described herein, improves the brightness and/or smoothness of the electrodeposited coating produced. In some cases, the brightening agent is a neutral species. In some cases, the brightening agent comprises a charged species (e.g., a positively charged ion, a negatively charged ion).

Those of ordinary skill in the art would be able to select the appropriate combination of ionic species, wetting agent, complexing agent and/or other additives (e.g., brightening agents) suitable for use in a particular application. Generally, the additives in a bath are compatible with electrodeposition processes, i.e., a bath may be suitable for electrodeposition processes. One of ordinary skill in the art would be able to recognize a bath that is suitable for electrodeposition processes Likewise, one of ordinary skill in the art would be able to recognize additives that, when added to a bath, would make the bath not suitable for electrodeposition processes.

In some cases, the operating range for the electrodeposition baths described herein is 5-100° C., 10-70° C., 10-30° C., 25-80° C., or, in some cases, 40-70° C. In some cases, the temperature is less than 80° C. However, it should be understood that other temperature ranges may also be suitable.

Methods of the invention may be advantageous in that coatings having various compositions may be readily produced by a single electrodeposition step. For example, a coating comprising a layered composition, graded composition, etc., may be produced in a single electrodeposition bath and in a single deposition step by selecting a waveform having the appropriate segments. The coated articles may exhibit enhanced corrosion resistance and surface properties.

It should be understood that other techniques may be used to produce coatings as described herein, including vapor-phase processes, sputtering, physical vapor deposition, chemical vapor deposition, thermal oxidation, ion implantation, spray coating, powder-based processes, slurry-based processes, etc.

In some embodiments, the invention provides coated articles that are capable of resisting corrosion, and/or protecting an underlying substrate material from corrosion, in one or more potential corrosive environments. Examples of such corrosive environments include, but are not limited to, aqueous solutions, acid solutions, alkaline or basic solutions, or combinations thereof. For example, coated articles described herein may be resistant to corrosion upon exposure to (e.g., contact with, immersion within, etc.) a corrosive environment, such as a corrosive liquid, vapor, or humid environment.

The corrosion resistance of coated articles may be assessed using tests such as ASTM B845, entitled “Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts” following the Class IIa protocol, may also be used to assess the corrosion resistance of coated articles. This test outline a procedure in which coated substrate samples are exposed to a corrosive atmosphere (e.g., a mixture of NO₂, H₂S, Cl₂, and SO₂). The mixture of flowing gas can comprise 200+/−50 ppb of NO₂, 10+/−5 ppb of H₂S, 10+/−3 ppb of Cl₂, and 100+/−20 ppb SO₂. The temperature and relative humidity may also be controlled. For example, the temperature may be 30+/−1° C., and the relative humidity may be 70+/−2%.

The exposure time of an article to a gas or gas mixture can be variable, and is generally specified by the end user of the product or coating being tested. For example, the exposure time may be at least 30 minutes, at least 2 hours, at least 1 day, at least 5 days, or at least 40 days. After a prescribed amount of exposure time, the sample is examined (e.g., visually by human eye and/or instrumentally as described below) for signs of change to the surface appearance and/or electrical conductivity resulting from corrosion and/or spotting. The test results can be reported using a simple pass/fail approach after the exposure time.

The coating subjected to the test conditions discussed above may be evaluated, for example, by measuring the change in the appearance of the coating. For instance, a critical surface area fraction may be specified, along with a specified time. If, after testing for the specified time, the fraction of the surface area of the coating that changes in appearance resulting from corrosion is below the specified critical value, the result is considered passing. If more than the critical fraction of surface area has changed in appearance resulting from corrosion, then the result is considered failing. For example, the extent of corrosive spotting may be determined. The extent of spotting may be quantified by determining the number density and/or area density of spots after a specified time. For example, the number density may be determined counting the number of spots per unit area (e.g., spots/cm²). The spot area density can be evaluated by measuring the fraction of the surface area occupied by the spots, where, for example, an area density equal to unity indicates that 100% of the surface area is spotted, an area density equal to 0.5 indicates that 50% of the surface area is spotted, and an area density equal to 0 indicates that none of the surface area is spotted.

In some cases, the coated article that is exposed to a mixed flowing gas according to ASTM B845, protocol Class IIa, for 5 days has a spotting area density of less than 0.10; in some cases, less than 0.05; and, in some cases, 0. In some embodiments, the coated article exposed to these conditions has a number density of spots of less than 3 spots/cm²; in some embodiments, less than 2 spots/cm²; and, in some embodiments, 0 spots/cm². It should be understood that spotting area densities and the number density of spots may be outside the above-noted ranges.

The low-level contact resistance of a sample may be determined before and/or after exposure to a corrosive environment for a set period of time according to one of the tests described above. In some embodiments, the low-level contact resistance may be determined according to specification EIA 364, test procedure 23. Generally, the contact resistivity of a sample may be measured by contacting the sample under a specified load and current with a measurement probe having a defined cross-sectional area of contact with the sample. For example, the low-level contact resistance may be measured under a load of 25 g, 50g, 150 g, 200 g, etc. Generally, the low-level contact resistance decreases as the load increases.

A threshold low-level contact resistance value may be set where measurement of a low-level contact resistance value for a sample above the threshold indicates that the sample failed the test. For example, the threshold low-level contact resistance value under a load of 25 g after 5 days exposure to mixed flowing gas according to ASTM B845, protocol Class IIa, may be greater than 1 mOhm, greater than 10 mOhm, greater than 100 mOhm, or greater than 1000 mOhm. It should be understood that other threshold low-level contact resistance values may be achieved.

In some embodiments, a coated article has reduced low-level contact resistance. Reduced low-level contact resistance may be useful for articles used in electrical applications such as electrical connectors. In some cases, an article may have a low-level contact resistance under a load of 25 g of less than about 100 mOhm; in some cases, less than about 10 mOhm; in some cases, less than about 5 mOhm; and, in some cases, less than about 1 mOhm. It should be understood that the article may have a low-level contact resistance outside this range as well. It should also be understood that the cross-sectional area of contact by the measurement probe may affect the value of the measured low-level contact resistance.

Durability of the coated articles may also be tested. In some embodiments, durability tests may be performed in conjunction with the corrosion tests discussed above and/or contact resistance measurements. A durability test may comprise rubbing the surface of a coated article with an object for a period of time and then visually inspecting the coating for damage and/or measuring the contact resistance of the coating. In one non-limiting example of a durability test, a counterbody may be held against the surface of a coated article at a set load and the coated article may be reciprocated such that the counterbody rubs against the surface of the coated article. For example, the counterbody may be held against the surface of a coated article at a load of 50 g. The duration of the reciprocal motion may be measured, for example, by the number of cycles per unit time per unit time. For instance, the reciprocal motion may be carried out for 500 seconds at a rate of 1 cycle per second. In some embodiments, durability may be measured before and/or after subjection of an article to a corrosion test as discussed in more detail above. The contact resistance of the coating may be measured as described above. In some cases, the coating may be visually inspected for wear tracks. The wear tracks may, in some embodiments, be analyzed by measuring the width of exposed base material between the wear tracks after a specific number of cycles under a specific load. In some instances, the analysis may be a “pass/fail” test, where a threshold width of exposed base material between wear tracks is set such that the presence of a width of exposed base material above the threshold indicates the article failed the test.

The following examples should not be considered to be limiting but illustrative of certain features of the invention.

EXAMPLES

All base materials for the following examples were cleaned and activated prior to electroplating using standard practices which would be familiar to one of ordinary skill in the art. The base material for all samples provided in the examples was Cu alloy 7025. Summaries of the example coatings and their performance metrics are shown in Tables 1 and 2.

Nanocrystalline NiW alloy deposits in the following examples were produced using a pulsed waveform and suitable bath chemistry operating at 60° C.

Nickel deposits in the following examples were produced using a DC current and nickel sulfamate plating chemistry operating at 60° C. and pH 3.8. The bath comprised Ni sulfamate at 431-533 g/L, NiCl₂-6H₂O at 14-21 g/L, and boric acid at 40-50 g/L.

Nanocrystalline AgW alloy deposits in the following examples were produced using a DC current and suitable bath chemistry operating at 50° C.

Rhodium deposits in the following examples were produced using a DC current and rhodium sulfate plating chemistry at 50° C. and pH 2.0. The bath comprised rhodium sulfate at 10 g/L rhodium metal and an organic brightening agent.

MFG class IIA testing refers to Mixed Flowing Gas test environment class IIA (ASTM B845).

Heat and humidity testing refers to a heat and humidity test conducted in an environmental chamber which maintains the temperature at 85° C. and the relative humidity at 85% RH using distilled water.

Dry heat testing refers to a dry heat test conducted in a constant temperature oven maintained at 150° C. for 1000 hours.

Neutral salt spray testing (NSST) refers to a neutral salt spray test conducted in an environmental chamber with a 5% sodium chloride salt fog per the ASTM B-117 standard test procedure.

Example 1

A series of flat coupons were cleaned, activated, and subsequently plated with 40 microinches of a nanocrystalline NiW alloy, and 80 microinches of a nanocrystalline AgW alloy. The set of coupons was subjected to each of the tests shown in Table 2. The results on these tests showed some level of discoloration or corrosion in all cases.

Example 2

A series of flat coupons were cleaned, activated, and subsequently plated with 40 microinches of a nanocrystalline NiW alloy, 80 microinches of a nanocrystalline AgW alloy, and 0.5 microinches of rhodium. The set of coupons was subjected to each of the tests shown in Table 2. The results on these tests showed some level of discoloration or corrosion distributed across the coupons in all cases.

Example 3

A series of flat coupons were cleaned, activated, and subsequently plated with 40 microinches of a nanocrystalline NiW alloy, 80 microinches of a nanocrystalline AgW alloy, and 1.5 microinches of rhodium. The set of coupons was subjected to each of the tests shown in Table 2. The result on the MFG test showed slight discoloration distributed across the coupons. The other test conditions showed no evidence of discoloration or corrosion.

Example 4

A series of flat coupons were cleaned, activated, and subsequently plated with 40 microinches of a nanocrystalline NiW alloy, 80 microinches of a nanocrystalline AgW alloy, and 3 microinches of rhodium. The set of coupons was subjected to each of the tests shown in Table 2. The results on the tests showed no evidence or discoloration or corrosion.

Example 5

A series of flat coupons were cleaned, activated and subsequently plated with 40 microinches of nickel, 80 microinches of a nanocrystalline AgW alloy, and 3 microinches of rhodium. The set of coupons was subjected to each of the tests shown in Table 2. The results on the tests showed no evidence or discoloration or corrosion.

Example 6

A series of flat coupons were cleaned, activated and subsequently plated with 40 microinches of a nanocrystalline NiW alloy, 80 microinches of a nanocrystalline AgW alloy, and 5 microinches of rhodium. The set of coupons was subjected to each of the tests shown in Table 2. The results on the tests showed no evidence or discoloration or corrosion.

Example 7

A series of flat coupons were cleaned, activated, and subsequently plated with 40 microinches of a nanocrystalline NiW alloy deposit, 80 microinches of a nanocrystalline AgW alloy deposit, and 10 microinches of rhodium. The set of coupons was subjected to the MFG and NSST tests shown in Table 2. The results on the tests showed localized corrosion. SEM/EDS inspection of samples prior to testing showed stress cracks in the Rhodium deposit.

TABLE 1 List of examples Rh AgW Alloy NiW Alloy Nickel Thickness Thickness Thickness Thickness Example (microinch) (microinch) (microinches) (microinches) 1 0 80 40 — 2 0.5 80 40 — 3 1.5 80 40 — 4 3 80 40 — 5 3 80 — 60 6 5 80 40 — 7 10 80 40 —

TABLE 2 Example performance Heat and MFG Class Humidity NSST Examples IIA 5 days (5 days) (96 hours) Dry Heat 1 Discoloration Corrosion Corrosion Discoloration 2 Discoloration Corrosion Corrosion Discoloration 3 Minor PASS PASS PASS discoloration 4 PASS PASS PASS PASS 5 PASS PASS PASS PASS 6 PASS PASS PASS PASS 7 Localized Not tested Localized Not tested discoloration corrosion 

1. An article comprising: a base material; a barrier layer formed on the base material; a metal layer formed on the barrier layer; and a Rh layer formed on the metal layer and having a thickness between about 1 microinch and about 5 microinches.
 2. The article of claim 1, wherein the barrier layer comprises silver.
 3. The article of claim 2, wherein the barrier layer comprises a silver-based alloy.
 4. The article of claim 1, wherein the barrier layer comprises nickel.
 5. The article of claim 4, wherein the barrier layer comprises a nickel-based alloy.
 6. The article of claim 5, wherein the nickel-based alloy further comprises tungsten and/or molybdenum.
 7. The article of claim 5, wherein the nickel-based alloy further comprises phosphorous.
 8. The article of claim 5, wherein the nickel-based alloy further comprises cobalt.
 9. The article of claim 5, wherein the nickel-based alloy further comprises palladium.
 10. The article of claim 1, wherein the barrier layer comprises palladium.
 11. The article of claim 1, wherein the barrier layer has a nanocrystalline grain size.
 12. The article of claim 1, wherein the metal layer has a nanocrystalline grain size.
 13. The article of claim 1, wherein the metal layer comprises a metal selected from the group consisting of Au, Ru, Os, Rh, Ir, Pd, Pt, and Ag.
 14. The article of claim 1, wherein the metal layer comprises a silver-based alloy.
 15. The article of claim 1, wherein the metal layer comprises a silver-based alloy and the barrier layer comprises a nickel-based alloy.
 16. The article of claim 1, wherein the metal layer comprises a silver-based alloy further comprising molybdenum and/or tungsten and the barrier layer comprises a nickel-based alloy further comprising molybdenum and/or tungsten.
 17. The article of claim 1, wherein the metal layer comprises a silver-tungsten alloy and the barrier layer comprises a nickel-tungsten alloy.
 18. The article of claim 1, wherein the Rh layer is formed directly on the metal layer.
 19. The article of claim 1, wherein the Rh layer is electrodeposited.
 20. The article of claim 1, wherein the Rh layer has a nanocrystalline grain size.
 21. The article of claim 1, wherein the base material comprises a conductive metal.
 22. A method comprising electrodepositing a barrier layer on a base material; electrodepositing a metal layer on the barrier layer; and electrodepositing a Rh layer on the metal layer, wherein the Rh layer has a thickness between about 1 microinch and about 5 microinches. 23-42. (canceled) 